The title tells you the premise but not the genre. And we won't either.

Man on a Ledge is a suspense thriller about a guy who threatens to jump to his death from the top of a high-rise building.

Sam Worthington is Nick Cassidy, an ex-cop and ex-con who was convicted of theft but who has just escaped from prison. For farfetched reasons that slowly become clear as the narrative proceeds, Nick becomes the guy described in the title when he checks into the Roosevelt Hotel in midtown Manhattan, orders room service, then crawls out the window onto the ledge and threatens to jump.

As she tries to do just that, fascinated New Yorkers -- although not nearly as many as would turn up in real life -- stare up at the drama unfolding many floors above, many of them fearing that he will jump while being disappointed if he doesn't.

And Lydia, while hoping to be more successful with this potential suicide than she was recently when one of her jumpers actually jumped, comes to suspect that there's something else entirely going on here: that is, that this man's threat to take his life by plunging downward is actually a distraction. He seems to have something to prove. But what?

Meanwhile, behind the scenes that quickly dominate the day's breaking-news coverage, compliments of ambitious and exploitive local reporters like the one played by Kyra Sedgwick, a drama of a different sort -- a heist drama involving a massive diamond -- is playing out, involving Jamie Bell as Nick's brother, Genesis Rodriguez as his girlfriend, Ed Harris as a sleazy real estate tycoon, and Anthony Mackie as Nick's ex-partner.

That nothing is quite what it seems, a familiar approach in this kind of thriller, is fine. We only wish that the eventual revelations were more interesting and satisfying.

Director Asger Leth (the documentary Ghosts of Cite Soleil) takes the reins of his first narrative feature, working from a convoluted screenplay by Pablo Fenjves that's not a who-dun-it but a how-dun-it.

Leth sets things up effectively enough, making us want to know the reasons behind the events in the early going. But we're never properly convinced that the protagonist is actually in danger -- to himself or anyone else.

And the resolution calls for a number of laughably unpersuasive moments that simply undermine what's left of the film's real-world credentials. And while it's acceptable for a movie to start off inscrutable and then provide explanations down the line, it's another thing altogether to resort to the ludicrous in the late going.

As for the acting, it's all over the map, with Banks up to the task, but the bland Worthington characteristically underemoting to a fault and the usually reliable Harris overacting like crazy. Most of the cast come off like actors who have taken gigs despite not believing a word of the screenplay they just agreed to interpret.

Man on a Ledge is an initially engrossing thriller that eventually jumps from a ledge of plausibility to the ground of preposterousness below.